In a Long Term Evolution (LTE) system and an LTE-Advance system, downlink physical layer control signaling includes downlink transmission related Downlink Grant (DL Grant) information needed to be acquired by a terminal and uplink transmission related Uplink Grant (UL Grant) information needed to be acquired by a UE to indicate various transmission related information such as positions of transmission resources, modulation and encoding modes etc. These physical layer control signaling is transmitted on a Physical Downlink Control channel (PDCCH). The physical layer control signaling here primarily refers to user dedicated control signaling of the physical layer.
In Release (R for short) 8/9 of the LTE system and R10 of the LTE-Advance system, the physical layer control channel for transmitting the physical layer control signaling is generally configured to be transmitted on first N Orthogonal Frequency Division Multiplexing (OFDM) symbols, and the N symbols are generally referred to as a control signaling transmission region.
Available transmission resources of the existing control signaling transmission region (first control signaling transmission region, or first control signaling region) are divided into multiple resource units of Control Channel Elements (CCEs), control information occupation resources are allocated with units being CCEs, and the resource units of CCEs here can further be subdivided into multiple REGs, and one CCE is comprised of multiple discontinuous Resource Element Groups (REGs). In general, 9 REGs constitute one CCE, and further, each REG is comprised of multiple basic resource units.
Dedicated control signaling and common control signaling are transmitted with resource units being CCEs, then are mapped onto corresponding REG resources, and are further mapped onto minimum Resource Elements (REs) of multiple Physical Resource Blocks (PRBs). The terminal generally performs blind detection by means of: calculating initial positions of dedicated control signaling and common control signaling. Here, the dedicated control signaling is primarily concerned:
TABLE ONEAggregation levels of blind detection of control signaling andthe number of blind detectionsBlind detection space Sk [L]Type of controlAggregationSize of blind detectionNumber of blindsignalinglevel Lspace [in CCEs]detections M [L]UE- dedicated166 (6/1) 2126 (12/2)482 (8/4) 8162 (16/8)common4164 (16/4)8162 (16/8)
It can be seen that control signaling transmission resources allocated by a user are discontinuous, which brings many difficulties to implementation of a closed-loop precoding technology in a multi-antenna system. Therefore, in the control signaling region, only the diversity technology can be used, and it is difficult to use the closed-loop precoding technology. The primary reason is that there are great difficulties in demodulation pilot design and channel state information feedback of the first control signaling region, and therefore the control signaling in the existing releases only supports discontinuous resource transmission and diversity technologies.
In releases after R10, in order to enhance a transmission capacity of the control channel and support control signaling of more users, it is considered in design to develop a new control channel region (a second control signaling transmission region, or a second control signaling region), and the control signaling transmission resources of the same UE may be continuous time-frequency resources, to support the closed-loop precoding technology, thereby enhancing the transmission performance of the control information.
The control signaling regions of new and old releases are shown in FIG. 1. This method allocates part of transmission resources in the Physical Downlink Shared Channel (PDSCH) transmission region of the original R8/9/10 to be used as a new control signaling transmission region, so that the closed-loop precoding technology is supported when the control signaling is transmitted, thereby enhancing the control signaling capacity and supporting control signaling of more users. The control channel transmitted in the second control signaling region may be referred to as a second control channel or an enhanced PDCCH (ePDCCH).
Some ePDCCH detection methods will be described in terms of detection of resource granularity, pilot ports of candidate positions of ePDCCH transmission (ePDCCH candidates), transmission modes etc.
In general, without additional information, the terminal is not notified of how many transmission resources will be occupied by the encoded and modulated control information, the base station will firstly notifies the terminal of an ePDCCH resource Region such as 4 PRB pairs, for example, FIG. 1 illustrates 4 of all PRB pairs of the whole bandwidth, or the transmission resources are determined by the terminal according to a UE ID or other UE specific parameters. The ePDCCH resource Region actually limits that control information transmitted on all ePDCCHs of the terminal can only be included in the Region. Of course, the control information will not necessarily occupy the Region completely.
The base station and the terminal can also appoint that a basic resource allocation unit is the minimum allocation granularity, and then further appoint sizes of several occupation resources, which are generally aggregations of one or more resource allocation units. Aggregation of N resource allocation units is referred to as aggregation level N. The base station can transmit the encoded and modulated control information in one of the sizes. The terminal will perform blind detection on the several further appointed resource sizes, which can also be referred to as detecting several appointed aggregation levels. In general, a basic resource unit eCCE is defined, which has similar functions as that of the previous CCEs. The eCCE in the second control region may use the definition of the CCE in the old releases or be defined by slightly amending the definition of the CCE in the old releases, or may also be newly defined, or may has a fixed size or a variable size.
The eCCEs may include Distributed eCCEs and Localized eCCEs, as shown in FIG. 2.
Then, the control signaling may define different aggregation levels based on the eCCE, for example, aggregation 1, 2, 4, 8, or 1, 2, 4, or 1, 3, 5, 7 etc. Then different aggregation levels represent different resource sizes. The terminal specifically performs the blind detection on the several aggregation levels
The UE performs detection on these candidates. Blind detection will be performed on the candidates one by one. In consideration of the complexity, the terminal can not detect all possible conditions, and therefore, there is a search space including some specified candidates under multiple aggregation levels. As shown in FIG. 3, one grid represents one L-eCCE, which is comprised of 2 eREGs. As shown in FIG. 4, one grid represents one eREG.
In the prior art, the EPDCCH resource Region has a fixed size, for example, N PRBs, or M eCCEs etc. However, in an actual system, there are some conditions which will make the REs of the eCCEs available for carrying control information become less, for example:
for a common subframe and a special subframe of a TDD system, numbers of available OFDM symbols are different, and REs of each eCCE available for carrying control information are different.
Numbers of OFDM symbols occupied by the PDCCH are different, and REs of each eCCE available for carrying control information are different.
For the MBSFN subframe and the non-MBSFN subframe, as CRSs of 24 REs are to be transmitted, the REs available for carrying control information are different.
For subframes with a CSI-RS pilot and without a CSI-RS pilot, the REs available for carrying control information are different.
In some cases, REs in the eCCE available for carrying control information will be less; while in some cases, REs available for carrying control information will be more. When the REs available for carrying control information is less, the EPDCCH resource Region is generally large, and the frequency domain diversity gain or the frequency domain selectivity scheduling gain will be fully developed after a larger number of detections; and when the REs available for carrying control information is more, the EPDCCH resource Region needs not to be too large. While in the related art, the EPDCCH resource Region has a fixed size, which will influence the performance.